It was all the rage on TPU when it came out not too long ago. Unless you have an insanely good system you won't be able to turn all the eye candy on, but I've definitely heard (and read) good things about the game itself.

Metro 2033 is amazing, as long as you keep some attention to the story, and as long as you realise that the stopping power of most firearms is far from great (of course, but some user reviews on the interweb suggest that some people don't realise that).

About how demanding the game is: it depends on how much details you want and your screen resolution. On non-HD screens and medium settings, it may run more or less (no super frame rates, but playable) with medium hardware (see my signature and system specs, btw I disabled Advanced PhysX).
On HD screens and/or visual quality in it's full glory with all the bells and whistles, it will definitely get very demanding. Especially with tesselation enabled.